1. Field of the Invention
The present invention relates to a gasket disposed at the connection part of members used under relatively severe conditions. More specifically, the present invention relates to a metallic sheet covered gasket suitably used as a gasket applied for a connection part in the engine or its exhaust system of a motor vehicle, which is subjected to great variations of temperature and to which a mechanical shock such as vibration or the like is repeatedly applied.
2. Description of Related Art
In the engine of a motor vehicle, there are several connection parts which are subjected to great variations of temperature and to which a mechanical shock such as vibration or the like is repeatedly applied. Examples of such connection parts include the connection part for connecting the cylinder block to the cylinder head, the connection part for connecting the exhaust manifold forming the engine exhaust system, to the cylinder block, the connection part for connecting the exhaust manifold to the catalyst converter, the connection part for connecting the catalyst converter to the muffler, and the like. Gaskets interposed at such connection parts are required to always maintain good sealing properties even though they are used under the severe conditions mentioned above.
As the gasket used under such severe conditions, there is known a metal-covered gasket in which a soft core member made of heat-resisting fibers such as asbestos fibers, ceramic fibers or the like, or expanded graphite, is covered with a metallic sheet.
In such a metal-covered gasket, the soft core member is excellent in heat resistance and cushioning properties, while the metallic sheet enhances rigidity. Accordingly, this metal-covered gasket is considered to be very useful to provide excellent sealing properties, as a gasket used in the engine or the exhaust system.
However, when there is used the gasket having the soft core member made of asbestos fibers, ceramic fibers, expanded graphite or the like, the contact pressure of the connection part is decreased thereby deteriorating the sealing properties of the gasket due to heating by the exhaust gas, vibration of the engine and vibration transmitted from the road surface. Further, in a high-temperature zone, the cushioning properties of the gasket are poor to lower the fitness of the gasket to the connection surface. This also causes the sealing properties of the gasket to be lowered.